1. Field of Invention
This invention relates in general to magnetic transducers for transferring information signals to and from a magnetic medium and, in particular, to an improved dual element read/write transducer.
2. Description of the Prior Art
Various types of magnetic transducers have been disclosed in the prior art for transferring data to and from magnetic storage media such as magnetic tapes, disks and drums. One type, referred to as an inductive read/write head, employs a core of magnetic material having an air gap which is positioned adjacent to the surface of the magnetic media. A coil is wound on the core so that by supplying current to the coil, flux flows around the core and across the air gap, subjecting the magnetic surface to a flux field. By providing relative movement between the air gap and the surface and reversing current direction, the surface is magnetized horizontally in one of two directions. The area where the direction changes is referred to as a magnetic transition. The transitions correspond to reversals of current in the coil and may represent binary data values.
In order to read flux transitions from a magnetic surface, relative movement is required between the surface and the air gap of the magnetic core so that a current corresponding to the rate of change of the flux in the core is induced in a coil wound on the core. A combined inductive read/write transducer is generally used since the functions are mutually exclusive and, hence, only one core is required.
The art recognizes many drawbacks of inductive heads in attempting to read data from a magnetic surface. The linear track density of modern day recording systems is, in fact, limited primarily by the ability to read the magnetic transitions and not in the ability of the transducer to record the data.
The prior art also discloses a magnetic transducer referred to as a magnetoresistive (MR) sensor or head which has been shown to be capable of reading data from a magnetic surface at linear densities much greater than can be achieved with an inductive read head. The MR sensor operates on the principle that the resistance of the read element is a function of the amount and direction of magnetic flux being sensed by the element. The art has, therefore, suggested and disclosed several magnetic transducers in which the inductive write element is provided in combination with an MR read element. The art further teaches that in order for an MR element to operate optimally, two bias fields should be provided. In order to bias the material so that its response to a flux field is linear, a transverse bias field is generally provided. This bias field is normal to the plane of the magnetic media and parallel to the surface of the planar MR element and, in practice, has been generated by various arrangements including simple permanent magnets or complex electromagnet type devices.
The other bias field sometimes employed with MR sensors is referred to in the art as the longitudinal bias field which extends parallel to the surface of the magnetic media and parallel to the lengthwise direction of the MR sensor. The longitudinal bias field may be applied by a permanent magnet or by a mechanism referred to in the art as an "exchanged coupling" which involves the interaction of the MR element per se with a parallel element supplied with the bias current. The function of the longitudinal bias field is to suppress Barkhausen noise.
The interest in dual element inductive-write, MR-read transducers has increased in recent years because of advances in thin film technology and the ability to make integrated magnetic heads in a manner similar to making integrated circuit chips. One such dual element transducer is shown in U.S. Pat. No. 3,975,772 in which the MR element is positioned between the legs of an inductive write transducer and one shield of a pair of shields is disposed between each leg and the MR element. This patent does not disclose either form of biasing of the MR element.
A means for transverse biasing the MR element of a dual element read/write transducer is shown in IBM Technical Disclosure Bulletin, Vol. 24, No. 4, Sept. 1981 by Lee and Tsang. In the drawing of that publication, which is reproduced as FIG. 1 in this application, the MR element is positioned in the air gap of the inductive write core that is defined by the two pole tips P1 and P2. The MR element 1 is canted relative to the gap defining surfaces of the pole tips so that the upper edge of the MR element is closer to the surface of the P1 pole tip than to the P2 pole tip, while the lower edge of the MR element is closer to P2 pole tip than to P1 pole tip. As a result of this canting and of the better permeability of the material of the MR element layer relative to air, the flux in the gap which would normally extend in a uniform manner across the gap between P1 and P2 tends to enter the M1 element at the top and flow through the element toward its lower edge. FIG. 1a shows field distribution of the element shown in FIG. 1. The flux which flows from P1 to P2 through the MR element during a read operation is sufficient to provide the transverse bias field for the MR element without affecting the data stored on the surface of the medium.
If the arrangement suggested in the referenced Technical Disclosure Bulletin is implemented in integrated thin film technology, the canting of the MR element involves laying down a thin film layer of air material at an angle relative to the rest of the films in the device, which are generally in parallel planes relative to each other. The added controls for establishing the canted layer eliminates much of the advantages originally obtained from using thin film technology in making dual element transducers.
The present invention discloses an arrangement in which the transverse bias field for the MR element disposed in the gap of an inductive write core may be obtained which avoids the thin film process problems involved in laying down a layer which is canted relative to the rest of the structure. In addition, this invention discloses a specific dual biasing scheme in which Barkhausen noise is suppressed via the exchange coupled longitudinal bias and a linear, sensitive MR response is achieved via a small current in the inductive write element which is applied during reading.